Film type packing element for use in cooling towers

ABSTRACT

A film-type packing element (1) for use in a cooling tower comprises a formable sheet material formed with corrugations (3) and ridge formations (5) extending obliquely of the direction of the corrugations (3) to provide deflection channels for fluid descending over the packing element. The ridge formations (5) are divided into a plurality of groups (9) along the corrugation direction, with the ridge formations (5) of successive groups (9) being angled oppositely relative to the corrugation direction.

BACKGROUND OF THE INVENTION

This invention relates to packing elements for heat exchange and masstransfer between liquid and gas phases of fluid, for use in, forexample, cooling towers. In particular this invention relates to regularor ordered packing elements formed from formable sheet material andhaving corrugations.

A common object in the design of any cooling tower pack is to provide apack with efficient heat exchange and mass transfer characteristics. Infulfilling this object it is important to maximise the surface area tovolume ratio of liquid on the pack and hence to effect an evendistribution of fluid over the pack. Uniform wetting is easily achievedin self-wetting woven wire fabric elements where capillary forces actbetween the fibres. One drawback of such elements is that they areexpensive to produce. In contrast, elements made from formable sheetmaterial such as Polyvinylchloride (PVC), Polythene etc. are muchcheaper to produce. However, designing a packing element from sheetmaterial which achieves a uniform distribution of liquid over thesurface of the sheet and thus efficient mass transfer from bulk liquidto film, is not a trivial matter, especially since capillary forces donot act between the liquid and sheet element as in the fabric elements.

Forming the sheets with folds or corrugations represents the most commonmethod of increasing the surface area. Liquid flowing over the sheets isspread laterally either by inclining the corrugations at an angle to thevertical or by forming the sheets with secondary perturbations, or byincorporating in the sheet a combination of both.

Regular packing elements consisting of corrugated sheets fixed togetherto form an array of parallel vertical passageways, such as inGB-A-2,093,967 and EP-A-28545, have a number of advantages over otherknown packing arrangements.

In a conventional cooling tower, liquid is sprayed onto the pack from anarray of horizontal plan sprays located above the pack. Packs whosepassageways are disposed at an angle to the vertical have shadowed areasat the entrance of the pack which cannot be wetted effectively, and inthe case of vertically falling liquid cannot be wetted at all. Thus, anadvantage of packs having vertically standing passageways is that everyunit area of the entry faces has an equal probability of being wetted.

In packs with slanted corrugations the liquid tends to concentrate intochannels defined by the corrugations, resulting in a non uniformdistribution of liquid over the pack. Furthermore, liquid flowing overthe corrugations is for part of the time suspended from above,increasing the probability of the liquid becoming dissociated from thesurface of the sheet. This loss of liquid results in a loss of thermalperformance. In contrast, packing elements having corrugationsvertically aligned do not suffer from either of these intrinsicproblems.

In natural-draft cooling towers operating in counter-flow mode the airflow is governed by the relation between the buoyancy forces and thepack impedance. A pack with vertical passageways will present lessimpedance to the air flow than packs which are inclined to the vertical,because the passageways run parallel to the air flow direction. By thesame argument, packs with horizontally disposed passageways present lessimpedance to the air flow in cross-flow cooling towers.

A still lower impedance is achieved for packs in which both thecross-sectional geometry of the corrugations forming the passageways andtheir cross-sectional area remain constant over the length of the pack.The impedance is further reduced if the passageways formed by thecorrugations are linear.

A lower impedance results in a lower pressure drop along the length ofthe packing element for a given air flow and, therefore, in a naturaldraught cooling tower, a larger air flow for a given buoyancy induceddriving force. This results in a more efficient heat exchange and masstransfer between the liquid and gas phases across the boundary layer forseveral reasons. Air flowing next to the boundary layer at any givenpoint will be cooler and less saturated than air having a lowervelocity, giving a larger thermal gradient across the layer resulting ina correspondingly higher rate of heat exchange. The faster air flow alsopromotes the diffusion of saturated air away from the boundary layernext to the water film, thus enhancing the evaporation rate, cooling theliquid further.

A further advantage of vertically disposed corrugated sheets is thatthey have considerable strength in the vertical, i.e. load bearingdirection.

Although packs comprising vertical corrugated sheets have certainadvantages as mentioned above, there remain a number of practicalproblems to be overcome, which may be solved with an appropriate design.

As mentioned above, it is common to employ an array of horizontal planjets to spray the liquid onto the pack. A common problem associated withthis water distribution apparatus is that liquid impinging on the top ofthe pack will have an uneven coverage across the pack. An object of thepresent invention is to provide a packing element which promotes fastand effective distribution of liquid from the top of the pack over arelatively short vertical distance, and thereafter to maintain an evencoverage as the liquid continues to propagate.

The liquid coolant in many cooling tower applications is water drawnfrom rivers, and is preferred because it is readily available andtherefore cheap. This water is usually contaminated with suspendedparticles of sedimentary deposits as well as other particulate orviscous contaminants. Use of such water in unpurified form exposes thepacking elements to the possibility of fouling. Initially the depositswill be trapped at points in the surface structure where the liquid iscaused to stagnate. In such regions the particles will tend to bedeposited and build up on the surface thus enhancing the stagnationregion and increasing the deposition. In time, this will causeessentially two problems. The deposits will form a layer, tending tosmooth over any surface structure, so that liquid is deflected to anever decreasing degree with the result that the patterned surface losesits effectiveness in distributing the liquid. In the worst case thelayer would destroy all surface structure, leaving a planar sheet. Thiswould drastically reduce the efficiency of the pack as well as increaseits overall weight. Furthermore, the build-up of fouling will begin torestrict the free space between neighbouring sheets, thereby increasingthe impedance to the air flow. This causes a reduction in air flow withconsequent loss of performance of the pack. Finally, if the fouling isgreat enough, the weight of it will compromise the structure of thecooling tower.

Another problem in designing a cooling tower pack is to provide anappropriate surface structure which compels the falling liquid to resideon the sheet for an adequate period of time (dwell time), so that theliquid is cooled effectively and sufficiently from the moment the liquidenters the pack to the time it reaches the bottom of the pack.Appropriate surface structure is essential in achieving this, butsurface structure tends to promote fouling. Thus, there is a trade-offbetween optimising the dwell time and reducing the possibility offouling to a minimal extent.

It is a further object of the present invention to provide a pack inwhich the dwell time of liquid on the pack can be optimised whilst atthe same time the possibility of fouling by deposits can be minimised,thereby prolonging the effectiveness and lifetime of the pack.

The problem to be solved is to provide a cooling tower pack whichfulfils all of the above mentioned objects.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda film-type packing element for use in a cooling tower comprising aformable sheet material formed with corrugations and ridge formationsextending obliquely of the direction of the corrugations to providedeflection channels for fluid descending over the packing element, theridge formations being divided into a plurality of groups along thecorrugation direction with the ridge formations of the successive groupsbeing angled oppositely relative to said direction.

Thus, by providing ridge formations extending obliquely of the directionof the corrugations wherein the ridge formations are divided into aplurality of groups with the ridge formations of successive groups beingangled oppositely relative to said direction, liquid descending thesheet will be given lateral momentum in the plane of the sheet, firstlyin one direction and so be entrained across the sheet, and secondly, onreaching the next group of ridge formations will be given lateralmomentum in the opposite direction. Thus, the liquid will be entrainedin a meander-like path as it propagates along the sheet. In this way,the liquid distribution over the pack is improved.

At the same time, because the ridge formations extend obliquely of thedirection of the corrugations, i.e. neither horizontally nor vertically,the possibility of stagnation of liquid descending the sheet, andtherefore fouling, is reduced. Furthermore, because the ridge formationsare in groups, the liquid is given a series of sideways kicks at eachridge formation. In this way the change of momentum imparted to theliquid is not so severe, so than the particles suspended therein aremore able to follow the path of the liquid. This also reduces thepossibility of fouling and hence prolongs the performance and life ofthe packing element.

Simultaneously the dwell time is made sufficient since each time theliquid interacts with a deflection channel it is decelerated in thevertical direction, counteracting the gravitational force on the liquidso that the fluid maintains an almost constant velocity along the sheet.The velocity is governed by such factors as the angle, height anddensity of the ridge formations, the volume of liquid and any capillaryforces acting between the liquid and the ridge formations. The angle anddensity of the ridge formations can be varied to optimise the dwelltime.

In a preferred embodiment, the packing element has an even number ofgroups of ridge formations over the dimension of the packing elementalong the corrugation direction. Thus, when a plurality of such elementsare installed in a cooling tower in such a manner that they are stackedone above the other, continuity of successive groups being angledoppositely is maintained. Additionally, it is preferred that each grouphas the same number of ridge formations so that sideways momentumimparted to the falling liquid tends to average out to zero (by symmetryconsiderations) over the dimension of the packing element along thecorrugation direction. This enhances uniformity of the liquid coverageacross the sheet and at the same time prevents liquid concentrating atthe side edges of the sheet.

Preferably, the ridge formations are formed to provide a zig-tag patterntransverse to the corrugation direction. This is particularlyadvantageous in crossflow cooling towers where the corrugations extendhorizontally, so that fluid flows transversely of the corrugationdirection.

Advantageously, the pitch of the zig-zag pattern can be variedindependently of the pitch of the corrugations depending on theapplication. For example, if in a particular application it is necessaryto maintain a sideways momentum in only one direction over aconsiderable width or over a greater vertical length in the case ofcross-flow cooling towers, the pitch of the zig-zag may extend over aplurality of corrugations. On the other hand, if good local cross mixingis of primary importance, the pitch of the zig-zag may be made equal toor less than the pitch of the corrugations.

In a preferred embodiment the ridge formations comprise discrete linearprotrusions in the sheet material which extend not more than half apitch of the corrugations. By providing gaps between the ridgeformations, liquid having been directed toward the gap will flow fasteralong the gap between the ridge formations, thereby reducing hold up andhence build up of liquid at this juncture.

Preferably, the corrugations have a generally triangular wave form withpeaks and troughs of the wave form clipped, so as to form flat portionsextending along the corrugation direction. Advantageously the flatportions provide gaps between the deflection channels so that liquid isnot concentrated in a V-shaped groove which would otherwise bedetrimental to the thermal performance of the sheet. This also providesa distance over which the liquid is not being acted upon by the ridgeformations so that the liquid transverse velocity decreases due tofriction between the sheet surface and the liquid, thereby giving thefluid an equal probability of being accelerated in any of the twolateral directions on reaching the next group.

In a preferred embodiment, groove formations are formed in the sheetperpendicular to the corrugation direction. Advantageously these can beinterspaced between successive groups and preferably have a semicircularcross-section so that vertical rigidity is maintained as far aspossible, whilst the vertical flow of fluid is not significantlyinterrupted.

The packing elements preferably include an array of integrally formedstand-offs and complementary sockets extending outwardly therefrom, andsituated on the flat portions defining the peaks and troughs of thecorrugations to maintain adjacent sheets at spaced relationship. It isdesirable to configure the array so that the pack is formed fromidentical sheets and by turning every other sheet through 180° thestand-offs fall opposite the sockets with all four edges of adjacentsheets aligned perpendicularly of the general plane of each sheet.

Accordingly, a second aspect of the present invention provides afilm-type packing element for use in a cooling tower comprising aformable sheet material formed with corrugations and having discretestand-off formations upstanding along ridge lines of the corrugations onone face of the sheet and discrete socket formations formed along otherridge lines of the corrugations on the other face of said sheet, andpositioned so as to engage each other when alternate sheets are rotatedsubstantially 180° in the plane of said sheets.

In a preferred embodiment of this second aspect of the presentinvention, the stand-off formations and discrete socket formations arespaced at successive ridge lines of the corrugations.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments of the present invention will now be describedwith reference to the drawings, in which:

FIG. 1 is an elevation view of a packing element according to apreferred embodiment of the present invention;

FIG. 2A shows an expanded elevation view of part of a group of discreteprotrusions shown in FIG. 1;

FIG. 2B shows a cross-section through a discrete protrusion along theline B--B;

FIG. 2C shows a cross-section of a protrusion along the line C--C;

FIG. 3 shows a cross-section of two neighbouring packing elements havinga generally triangular wave form and spaced apart at discrete points inaccordance with a preferred embodiment;

FIG. 4A shows a side view of the stand-off and socket arrangement shownin FIG. 3, and includes a cross-sectional view of the groove formationsin accordance with a preferred embodiment;

FIG. 4B shows an elevation view of the stand-off and socket arrangementshown in FIG. 4A;

FIG. 4C shows a cross-section through the line C--C in FIG. 4A;

FIG. 5 is a side view of the groove formation shown in FIG. 4A,extending in phase with and transverse to the corrugation direction;

FIG. 6 shows an elevation view of a packing element including a joinparallel to the corrugation direction in accordance with a preferredembodiment; and

FIG. 7 shows a cross-sectional view of an assembled pack comprisingsheet elements of the preferred embodiment shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 to 3, a film-type packing element 1 for use in acounter flow cooling tower comprises a formable sheet material formedwith corrugations 3 and ridge formations 5 extending obliquely of thedirection of the corrugations to provide deflection channels 7 for fluiddescending generally along the corrugations 3. The ridge formations aredivided into a plurality of groups 9 along the corrugation direction.Ridge formations of successive groups are angled oppositely relative tothe corrugation direction. The dimension of the packing element alongthe corrugation direction and the width transverse to the corrugationdirection are typically 0.6 m and 2.37 m respectively. This embodimentfurther comprises a number of preferred features which have beencarefully refined (after much research) for optimum performance in acooling tower under normal load conditions, whilst still retaining highperformance for conditions deviating significantly from the norm. Thepreferred directions of liquid and air flow over the packing element ina counterflow cooling tower are shown by arrows in FIG. 1.

Referring to FIG. 3, the corrugations have a generally triangular waveform with the peaks 11 and troughs 13 of the wave form clipped so as todefine flat portions 15 and 17, also shown in FIG. 1. The corrugationamplitude and wavelength are typically 19 mm. and 57 mm. respectively,although these dimensions may be varied to change the free space to packvolume ratio. The flats are typically between 6 mm. and 7 mm. wide. Thecross-sectional geometry is substantially invariant along the length ofthe packing element. In use, the sheets are preferably alignedvertically, parallel to the general direction of descending liquid,although some applications may demand the sheets to be either inclinedor disposed horizontally, for maximum performance. Such a situation mayarise in cross flow cooling towers.

The packing element comprises six groups 9 of ridge formations 5 overthe dimension of the packing element along the corrugation direction,with each group 9 having a plurality, for example seven, ridgeformations 5. The ridge formations are formed to provide a zig-zagpattern transverse to the corrugation direction and extend over thewidth of the sheet 1. In this embodiment the pitch of the zig-zagpattern is constant and equal to the pitch of the corrugation. However,the pitch of the zig-zag pattern may vary over the width of the sheet,and may be greater or less than the pitch of the corrugations. At thesame time the zig-zag pattern is in phase with the corrugations andalthough this feature is preferred it is not essential to the invention.

The ridge formations 5 are preferably discrete linear protrusions 6, asshown in FIGS. 1 and 2, each protrusion extending over not more thanhalf the pitch of the corrugations. In the embodiment shown, theprotrusions 6 extend between the boundaries defined by the flat portionsof neighbouring peaks and troughs of the corrugations. Because thepacking element is formed from formable sheet material such aspolyvinylchloride (PVC), polythene or metal foil etc., the reverse sidewill have the negative form of the side shown. Thus, the ridges on oneside will define depressions on the other side. In FIG. 1, theprotrusions extend upwards from the plane of the figure, defining side`A` of the sheet. In FIG. 3, side `A` is inverted, and so facesdownwards, with side `B` facing upwards as shown. Although the ridgeformations 5 are discrete linear protrusions, they may also becontinuous across the width of the sheet and so have the form of zig-zagsecondary corrugations.

FIGS. 2A through 2C show an expanded view of part of a group 9 ofdiscrete protrusions. Each protrusion 6 is elongate and Linear with theends being semi-circular. The ends of each protrusion are also curved inthe direction perpendicular to the sheet as shown in FIG. 2B. Theoverall length of the protrusion is typically 33 mm. In cross-section,the protrusions are semi-circular with a diameter of typically 6-7 mm.and define similarly shaped depressions on the other side of the sheetas shown in FIG. 2C. The protrusions of each group are parallel to oneanother and spaced apart to define deflection channels having widths ofthe same order of magnitude as the widths of each protrusion. Theoptimum angle, 2 r between each protrusion and the corrugation directionhas been found to be substantially 60°.

The rounded nature of the protrusions serves to ease the flow of liquid,reducing the number of sites in which fluid could stagnate or in whichdeposits may collect. In addition, where the sheets are fabricated byvacuum forming, the rounded profile ensures that weak points delineatedby sharp or abrupt edges, are kept to a minimum. Furthermore, theprotrusions increase the rigidity and strength of the linear corrugationpanels 19 between neighbouring troughs and peaks in directions bothparallel and transverse to the corrugation direction. Thus, the overallstiffness and load bearing capability of the packing element isconsiderably enhanced.

It should be noted that the protrusions are not limited to anyparticular shape. Indeed, the ridge formations at the ends of each group9 may have other shapes in order to increase the surface area of thepacking element.

To illustrate how the packing element effects liquid distribution overthe surface thereof, and to simplify explanation of a complex irrigationprocess, it is worth considering one particular scenario. Referring toFIG. 1, we first assume that a single unit of liquid starts at the topedge of the sheet at position A9. As the unit of liquid descends itinteracts with the protrusions which impart sideways momentum to theliquid in opposite directions. As a result, the unit of liquid separatesinto two roughly equal portions. At each protrusion the liquid will begiven a small sideways kick so that it spreads into a film across thewidth of the corrugation. On reaching flat portions 15, the liquid is nolonger acted upon by the protrusions and so will tend to flow parallelto the corrugation direction. Any liquid which has sufficient momentumto overshoot the flat portions before reaching the bottom of the firstgroup 9A of the ridge formations, will be directed back onto the flats15. The shape of the surface of the packing element is intended topromote these flow paths whilst presenting as few obstructions to theflow as possible. This assists in reducing hold-up, stagnation andsubsequent fouling by deposits which separate from the liquid.

At the second group of ridge formations, liquid an positions B8 and B10will have an equal probability of being deflected to the left or to theright. Accordingly, after descending the length of the second group 9Bthe liquid will have spread across a width corresponding to twowavelengths of the corrugations and in this simulation will bedistributed with proportions of 1/4, 1/2, 1/4 at points C7, C9 and C11respectively After travelling the length of the third group 9C theliquid will have spread over a width corresponding to three wavelengthsof corrugations, after four groups the liquid will have spread over fourwavelengths and so on. Thus to generalise, the lateral spread of liquidis increased by one corrugation wavelength after travelling one grouplength. From this illustration it is possible to appreciate how quickand effective irrigation over the packing element is achieved.Continuing the simulated sequence of irrigation, on reaching the bottomof the sheet the unit of liquid will span six corrugation wave lengthsand have concentrations equal to 1/64, 3/32, 15/64, 5/16, 15/64, 3/32and 1/64 at positions G3, G5, G7 . . . to G15.

This fan-like irrigation process serves several purposes. Firstly, inthe situation whereby liquid impinges on a concentrated region at thetop of the packing element, the sheet effects a fast lateral spread offluid across the width of the sheet, whilst at the same time ensuringthat the concentration is not depleted at the centre of the spread. Thisis due to the fact that whilst liquid is being spread in oppositedirections across the sheet it is also being directed back into thecentre because at each point on a line on the sheet denotedalphanumerically in FIG. 1, fluid has an equal probability of flowingeither to the right or to the left. Secondly, it can be appreciated thatif the liquid is distributed over the pack at equally spaced points withequal concentrations, a fan-like spread of liquid will result from eachpoint. This ensures that good cross mixing of liquid is achieved whilstat the same time an almost constant concentration of liquid across thesheet at any vertical point is maintained as the liquid continues topropagate. The above illustration is only one of many possible scenarioswhich may occur in practice. In general the sheet, by a statisticalpercollation process, will transform a random concentration of liquidstarting at the top edge of the sheet, into an even concentration ofliquid across the sheet, as the liquid descends.

FIG. 3 shows two identical sheets assembled to provide passagewaystherebetween, the cross-section of passageways having generally rhombicgeometry. The sheets are spaced apart at a predefined distance bydiscrete stand-offs 21 distributed at intervals along flat portions 15defining the peaks of the corrugations. The presence of this spacing isimportant since it allows the free flow of water in the transversedirection.

The stand-offs 21 are integrally formed with the sheet and definedepressions on the other side of the sheet. Complimentary sockets 25 areformed an intervals along the flat portions 17 defining the troughs ofthe corrugations and are positioned such that when every other sheet isrotated 180° in the plane of the sheen the stand-offs and socketsengage. To achieve this with an identical set of sheets, stand-offs 21are formed on each adjacent peak 11 and sockets 25 are formed betweenthem on each adjacent trough 13. The sheen is formed so that opposededges 31 and 33, parallel to the corrugation direction, neighbour atrough 13A and a peak 11A respectively. The stand-offs 21 extendtypically 8 mm. from the flats 15, and the sockets have a depth suchthan the spacing between flats of opposed sheets is typically 6 mm.

Referring to FIG. 4A through 4C, the stand-offs 21 are elongate with thelonger side parallel to the corrugation direction. The end walls 22 aresemi-circular in cross-section in accordance with FIG. 4B and also slopeinwards so that the base 23 of each stand-off is longer than the top 24.The lengths of the base 23 and top 24 are typically 25 mm. and 20 mm.respectively. This stream lined shape is preferred since it both reducesair flow drag and the possibility of fouling at these points. Inaddition the inner walls of the stand-offs on the reverse side of thesheet are shaped to ease the flow of liquid to reduce the possibility ofliquid stagnating in the cavity. The sockets 25 in which the stand-offsare seated are considerably longer than the top of the stand-offs toassist in alignment during the manufacturing process.

Mating surfaces of the stand-offs and sockets are bonded together bygluing or welding, etc. during pack assembly. In the preferredembodiment shown in FIG. 1, the stand-offs 21 are positioned betweeneach of the groups of ridge formations 9. The purpose of this is toensure that at some point along each group, water is deflected from theflats 15 and 17 into deflection channels either side, which assists inthe liquid distribution process.

Referring to FIGS. 4A and 5, transverse groove formations 27 runningperpendicular to the corrugation direction are formed in the sheet andpreferably disposed between each group 9 as shown in FIG. 1. The grooveformations enhance the rigidity of the packing element transverse to thecorrugation direction. They are preferably semi-circular in profile sothat the sheet retains its compressional strength in the direction ofthe corrugations. On the reverse side of the sheet the groove formationsappear as semi-circular humps over which the liquid traverses withminimal effort. The diameter of the groove formations is typically 4 mm.

As will be appreciated, the above described embodiment has thecharacteristic of minimising the effect of fouling on its performance.Firstly, the rate of build up of fouling is minimized by the avoidanceof structures which would cause the water flow to stagnate. Secondly,because the passageways formed by the corrugations are linear, and thesurface structure relied upon to effect the liquid distribution does notsignificantly modify this linearity, any fouling that does occur willimpede the air flow to a minimal extent.

FIG. 6 shows an elevation of part of a packing element, and exemplifiesa land 29 running parallel to the length of the sheet, made to extendthe sheet width. In a preferred form of manufacture the sheets will beformed in sections from one land to another but will be separated fromthe formed pvc only at every alternate land, thus leaving half-lands 31and 33 at each edge of the sheet and a full land in the middle. The landoccurs between a peak and trough of corrugations at a distance from theedge of the sheen of typically 1.18 m. This method ensures that gluingor welding points of adjacent sheets do not occur on the edge of thesheets and thus provides a stronger joint and is to be preferred.

To facilitate assembling the sheets to form a pack as shown in FIG. 7,it is preferable to cut the sheets so that the edges of the sheetsparallel to the corrugation direction are formed between a peak andtrough with opposed edges 31 and 33 in FIG. 3 neighbouring a trough anda peak respectively. This is so that when every other sheet of anidentical set of sheets is rotated 180°the edges of adjacent sheets arealigned and form a strong pack face perpendicular to the general planeof the sheets.

A particularly advantageous property of the above described embodimentis that of low air flow impedance. This is due to several factorsincluding the linear nature of the passageways formed by thecorrugations and the substantial invariance of their cross-sectionalgeometry. However, an especially significant factor is the relativelyhigh free space to pack volume ratio which can be achieved asappreciated from FIG. 7. This is made possible by imparting appropriatestructure to the pack to increase its rigidity and strength per unitarea in directions both transverse and parallel to the corrugationdirection, without requiring extra material. In this particularembodiment, the structure includes groups of oblique protrusions formedalong the corrugations and groove formations formed tranverse of thecorrugations. A pack requiring less material per unit volume has theadditional advantages of reduced weight and reduced cost.

Although embodiments of the present invention have been described withreference to counterflow cooling towers, these or similar embodimentsmay also be used in cross-flow cooling towers. In this application, thepack is preferably orientated such that the corrugations run parallel tothe cross-flow of air, i.e. horizontally, so that the pack presentsleast possible impedance to the air flow. With the corrugations disposedhorizontally, in a preferred embodiment, the ridge formations will forma vertically running zig-zag pattern defining oblique deflectionchannels which change direction every half wavelength of thecorrugations. In use, liquid descending a packing element will propagatein a meander-like path, changing direction every half wavelength ofcorrugation. This liquid distribution process is very similar to thatwhen the pack is used in a counterflow cooling tower i.e., thecorrugations are aligned vertically. It will therefore be appreciatedthat many of the advantageous properties of this pack when used incounterflow cooling towers, are carried over when the pack is used incrossflow cooling towers. This considerably enhances the versatility ofthe pack. In the special application where the pack is used as a hybridpack, in which some of the packing elements remain dry, the pack may bemodified to prevent liquid wetting these elements. As mentioned abovethe amplitude and wavelength of the corrugations as well as thedimensions and density of the ridge formations, may be varied dependingon the application and position of a pack within the cooling tower. Thismay just be a matter of scaling a particular embodiment up or down. Forexample, it may be desirable to use packs having a larger surface areanext to the liquid distribution apparatus. This may be achieved simplyby scaling the pack down to increase the corrugation density. Thescaling process will, however, also increase the density of the ridgeformations. If this is undesirable, the ridge formation density may bechanged independently of the corrugation density.

What is claimed is:
 1. A film flow packing element for use in a coolingtower comprising a formable sheet material formed with corrugations andridge formations extending obliquely of a direction parallel to a linealong a peak of the corrugations to provide deflection channels forfluid descending over the packing element, the ridge formations beingdivided into a plurality of groups along said direction with the ridgeformations of successive groups being angled oppositely relative to saiddirection, wherein the ridge formations extend over less than a pitch ofthe corrugations between a peak and a neighboring trough thereof.
 2. Afilm flow packing element as claimed in claim 1, comprising an evennumber of groups over the dimension of the packing element along saiddirection.
 3. A film flow packing element as claimed in claim 1, whereineach group has the same number of ridge formations.
 4. A film flowpacking element as claimed in claim 1, comprising at least four groups.5. A film flow packing element as claimed in claim 1, wherein the ridgeformations are formed to provide a zig-zag pattern transverse to saiddirection.
 6. A film flow packing element as claimed in claim 5, whereinthe pitch of the zig-zag pattern is equal to a whole number times thepitch of the corrugations.
 7. A film flow packing element as claimed inclaim 6, wherein the whole number is one.
 8. A film flow packing elementas claimed in claim 1, wherein the ridge formations comprise discretelinear protrusions in said sheet material.
 9. A film flow packingelement as claimed in claim 1, wherein the corrugations have a generallytriangular wave form.
 10. A film flow packing element as claimed inclaim 1, wherein the peaks and troughs of said wave form are clipped soas to form flat portions extending along said direction.
 11. A film flowpacking element as claimed in claim 1, including transverse grooveformations perpendicular to said direction.
 12. A film flow packingelement as claimed in claim 11, wherein the groove formations as locatedbetween successive said groups of ridge formations.
 13. A film flowpacking element as claimed in claim 1, including discrete stand-offformations upstanding along ridge lines of the corrugations on one faceof the sheet and discrete socket formations formed along other ridgelines of the corrugations on the other face on said sheet, andpositioned so as to engage each other when alternate sheets are rotatedsubstantially 180° in the plane of said sheets.
 14. A film flow packingelement as claimed in claim 13, having at least one stand-off formationdisposed between successive said groups.
 15. A film flow packing elementas claimed in claim 13, including transverse groove formations extendingperpendicular to said direction, wherein at least one stand-offformation is formed between successive groove formations.
 16. A filmflow packing element as claimed in claim 13, wherein said stand-offformations and said discrete socket formations are spaced alternately atsuccessive ridge lines of the corrugations.
 17. A film flow packingelement as claimed in claim 1, wherein edges of the sheet parallel tosaid direction are formed between a peak and a trough of saidcorrugations wherein opposed edges neighbor a trough and a peakrespectively.
 18. A film-flow packing element as claimed in claim 7,wherein each peak or trough of the zig-zag coincides with a peak ortrough of said corrugation.
 19. A film flow packing element as claimedin claim 13, wherein said stand-off and socket formations are sized sothat when the stand-off formations of one sheet engage the socketformations of an adjacent sheet, the ridge lines on which those socketand stand-off formations are formed are maintained in spacedrelationship.
 20. A film flow packing element for use in a cooling towercomprising a formable sheet material formed with corrugations and ridgeformations extending obliquely of the direction parallel to a line alonga peak of the corrugations to provide deflection channels for fluiddescending over the packing element, the ridge formations being dividedinto a plurality of groups along said direction with the ridgeformations of successive groups being angled oppositely relative to saiddirection, wherein the ridge formations are formed to provide a zig-zagpattern transverse to said direction with each peak or trough of thezig-zag substantially coinciding with a peak or trough of saidcorrugation.
 21. A film flow packing element as claimed in claim 20,comprising an even number of groups over the dimension of the packingelement along said direction.
 22. A film flow packing element as claimedin claim 20, wherein each group has the same number of ridge formations.23. A film flow packing element as claimed in claim 20, comprising atleast four groups.
 24. A film flow packing element as claimed in claim20, wherein the ridge formations comprise discrete linear protrusions insaid sheet material.
 25. A film flow packing element as claimed in claim20, wherein the corrugations have a generally triangular waveform.
 26. Afilm flow packing element as claimed in claim 25, wherein the peaks andtroughs of said waveform are clipped so as to form flat portionsextending along said direction.
 27. A film flow packing element for usein a cooling tower comprising a formable sheet material formed withcorrugations and having discrete stand-off formations upstanding alongridge lines of the corrugations on one face of the sheet and discretesocket formations formed along other ridge lines of the corrugations onthe other face of said sheet, and positioned so as to engage each otherwhen alternate sheets are rotated substantially 180° in the plane ofsaid sheets, said socket and stand-off formations being sized so thatwhen the stand-off formations of one sheet engages the socket formationsof an adjacent sheet, the ridge lines on which those socket andstand-off formations are formed are maintained in spaced relationship.28. A film flow packing element for use in a cooling tower comprising aformable sheet material formed with corrugations and having discretestand-off formations upstanding along ridge lines of the corrugations onone face of the sheet and discrete socket formations formed along otherridge lines of the corrugations on the other face of said sheet, andpositioned so as to engage each other when alternate sheets are rotatedsubstantially 180° in the plane of said sheets, wherein edges of thesheet parallel to said ridge lines are formed between a peak and atrough of said corrugations wherein opposed edges neighbor a trough anda peak respectively.